buddhuu, of course it is possible to accompany the song in different ways, you could lose the minors, and the F major, and do the 3 chord trick, it would "work" but you would lose a lot of the flavour.

What is a given is that the chord in the first bar is a D, not a G, as your colleague suggested.

Try doing an instrumental lead-in playing the melody of the last line, and you will see that a G is impossible in the opening bar, it has to be a D.